Solid electrolyte material and battery using same

ABSTRACT

The solid electrolyte material of the present disclosure includes Li, Ca, Y, Sm, X, and O, wherein X is at least one selected from the group consisting of F, Cl, Br, and I.

BACKGROUND 1. Technical Field

The present disclosure relates to a solid electrolyte material and abattery using it.

2. Description of the Related Art

Japanese Unexamined Patent Application Publication No. 2011-129312discloses an all solid state battery using a sulfide solid electrolyte.International Publication No. WO 2018/025582 discloses a solidelectrolyte material represented by Li_(6-3z)Y_(z)X₆ (0<z<2 issatisfied, and X is Cl or Br).

SUMMARY

One non-limiting and exemplary embodiment provides a solid electrolytematerial having a high lithium ion conductivity.

In one general aspect, the techniques disclosed here feature a solidelectrolyte material including Li, Ca, Y, Sm, X, and O, where X is atleast one selected from the group consisting of F, Cl, Br, and I.

The present disclosure provides a solid electrolyte material having ahigh lithium ion conductivity.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a battery according to a secondembodiment;

FIG. 2 is a graph showing X-ray diffraction patterns of solidelectrolyte materials of Examples 1 to 4;

FIG. 3 is a schematic view of a compression molding die used forevaluation of the ion conductivity of a solid electrolyte material;

FIG. 4 is a graph showing a Cole-Cole plot obtained by impedancemeasurement of the solid electrolyte material of Example 1; and

FIG. 5 is a graph showing the initial discharge characteristics of thebatteries of Example 1 and Comparative Example 1.

DETAILED DESCRIPTIONS

Embodiments of the present disclosure will now be described withreference to the drawings. First embodiment

The solid electrolyte material according to a first embodiment includesLi, Ca, Y, Sm, X, and O. Here, X is at least one selected from the groupconsisting of F, Cl, Br, and I.

The solid electrolyte material according to the first embodiment has ahigh lithium ion conductivity. Here, the high lithium ion conductivityis, for example, 1×10⁻⁵ S/cm or more. That is, the solid electrolytematerial according to the first embodiment can have, for example, an ionconductivity of 1×10⁻⁵ S/cm or more.

The solid electrolyte material according to the first embodiment can beused for obtaining an all solid state battery having excellent chargeand discharge characteristics. The all solid state battery may be aprimary battery or a secondary battery.

The solid electrolyte material according to the first embodimentdesirably does not contain sulfur. A solid electrolyte material notcontaining sulfur does not generate hydrogen sulfide, even if it isexposed to the atmosphere, and is therefore excellent in safety. Thesulfide solid electrolyte disclosed in Japanese Unexamined PatentApplication Publication No. 2011-129312 may generate hydrogen sulfidewhen it is exposed to the atmosphere.

The solid electrolyte material according to the first embodiment mayconsist essentially of Li, Ca, Y, Sm, X, and O. The phrase “the solidelectrolyte material according to the first embodiment consistsessentially of Li, Ca, Y, Sm, X, and O” means that the molar proportion(i.e., molar fraction) of the sum of the amounts of Li, Ca, Y, Sm,

X, and O to the sum of the amounts of all elements constituting thesolid electrolyte material in the solid electrolyte material accordingto the first embodiment is 90% or more.

As an example, the molar proportion may be 95% or more. The solidelectrolyte material according to the first embodiment may consist ofLi, Ca, Y, Sm, X, and O only.

In order to enhance the ion conductivity of the solid electrolytematerial, X may be Cl and Br.

In order to enhance the ion conductivity of the solid electrolytematerial, the solid electrolyte material according to the firstembodiment may further include at least one selected from the groupconsisting of Gd, Sr, Ba, Al, Sc, Ga, Bi, La, Zr, Hf, Ta, and Nb.

The transition metal included in the solid electrolyte materialaccording to the present embodiment may be only Y and Sm excludingelements included as inevitable impurities.

The X-ray diffraction pattern of the solid electrolyte materialaccording to the first embodiment can be obtained using Cu-Kα rays. Inthe obtained X-ray diffraction pattern, peaks may be present indiffraction angle 2θ ranges of 14.9° or more and 16.0° or less, 16.2° ormore and 17.4° or less, 22.3° or more and 23.5° or less, 28.1° or moreand 29.2° or less, 30.0° or more and 31.2° or less, 32.1° or more and33.3° or less, 39.2° or more and 40.3° or less, 47.0° or more and 48.1°or less, and 51.5° or more and 52.6° or less. Such a solid electrolytematerial has a high ion conductivity.

In order to enhance the ion conductivity of the solid electrolytematerial, the following four mathematical expressions may be satisfied:

2.6≤x≤3.4;

0.09≤y≤0.11;

1.2≤z≤2.1; and

2.7≤w≤4.4,

wherein,

x represents a molar ratio of Li to the sum of Y and Sm;

y represents a molar ratio of Ca to the sum of Y and Sm;

z represents a molar ratio of Br to the sum of Y and Sm; and

w represents a molar ratio of Cl to the sum of Y and Sm.

In order to further enhance the ion conductivity of the solidelectrolyte material, the following four mathematical expressions may besatisfied:

2.9≤x≤3.1;

0.09≤y≤0.11;

1.3≤z≤1.9; and

3.0≤w≤4.0.

In order to enhance the ion conductivity of the solid electrolytematerial, the molar ratio of O to the sum of Y and Sm may be greaterthan 0 and 0.36 or less.

In order to enhance the ion conductivity of the solid electrolytematerial, in the solid electrolyte material according to the firstembodiment, the molar ratio of O to the sum of Y and Sm may be greaterthan 0 and 0.08 or less. The molar ratio of O to the sum of Y and Sm maybe greater than 0 and 0.04 or less. The molar ratio of O to the sum of Yand Sm may be greater than 0 and 0.01 or less.

The shape of the solid electrolyte material according to the firstembodiment is not limited. Examples of the shape are needle, spherical,and oval spherical shapes. The solid electrolyte material according tothe first embodiment may be a particle. The solid electrolyte materialaccording to the first embodiment may be formed so as to have a pelletor planar shape.

When the shape of the solid electrolyte material according to the firstembodiment is a particulate shape (e.g., spherical), the solidelectrolyte material according to the first embodiment may have a mediandiameter of 0.1 μm or more and 100 μm or less. The median diameter meansthe particle diameter at which the accumulated volume in a volume-basedparticle size distribution is equal to 50%. The volume-based particlesize distribution can be measured with, for example, a laser diffractionmeasurement apparatus or an image analyzer.

In order to enhance the ion conductivity of the solid electrolytematerial according to the first embodiment and to well disperse thesolid electrolyte material according to the first embodiment and anactive material, the median diameter may be 0.5 μm or more and 10 μm orless.

Method for Manufacturing Solid Electrolyte Material

The solid electrolyte material according to the first embodiment can bemanufactured by the following method.

First, raw material powders are provided so as to give a targetcomposition and are mixed.

When a solid electrolyte material consisting of Li, Ca, Y, Sm, Br, Cl,and O is produced, a LiCl raw material powder, a LiBr raw materialpowder, a YCl₃ raw material powder, a SmCl₃ raw material powder, andCaBr₂ are mixed. The resulting powder mixture is heat-treated in aninert gas atmosphere with adjusted oxygen concentration and moistureconcentration (for example, an argon atmosphere having a dew point of−60° C. or less). The heat treatment temperature may be, for example,within a range of 200° C. or more and 650° C. or less. The resultingheat treatment product is left to stand in an atmosphere having arelatively high dew point (for example, a dry atmosphere having a dewpoint of −30° C.).

Subsequently, heat treatment is performed, for example, in an inert gasatmosphere with adjusted oxygen concentration and moisture concentration(for example, an argon atmosphere having a dew point of −60° C. or less)at a temperature of the melting point or more (for example, 500° C.). 0can be present in the entire solid electrolyte material by heattreatment at a temperature of the melting point or more. The rawmaterial powders may be mixed at a molar ratio adjusted in advance so asto offset a composition change that may occur in the synthesis process.The oxygen amount in a solid electrolyte material is determined byselecting the raw material powders, the oxygen concentration in theatmosphere, the moisture concentration in the atmosphere, and thereaction time. Thus, the solid electrolyte material according to thefirst embodiment is obtained.

The heat treatment product obtained by the first heat treatment may beused as the solid electrolyte material according to the firstembodiment.

The raw material powders to be mixed may be an oxide and a halide. Forexample, as the raw material powders, Y₂O₃, Sm₂O₃, NH₄Cl, NH₄Br, LiCl,LiBr, CaCl₂, and CaBr₂ may be used.

It is inferred that the oxygen constituting the solid electrolytematerial according to the first embodiment is incorporated from theabove-mentioned atmosphere having a relatively high dew point. Secondembodiment

A second embodiment will now be described. The matters described in thefirst embodiment may be appropriately omitted.

The battery according to the second embodiment includes a positiveelectrode, a negative electrode, and an electrolyte layer. Theelectrolyte layer is disposed between the positive electrode and thenegative electrode. At least one selected from the group consisting ofthe positive electrode, the electrolyte layer, and the negativeelectrode contains the solid electrolyte material according to the firstembodiment.

The battery according to the second embodiment contains the solidelectrolyte material according to the first embodiment and therefore hasexcellent charge and discharge characteristics.

FIG. 1 shows a cross-sectional view of a battery 1000 according to thesecond embodiment.

The battery 1000 includes a positive electrode 201, an electrolyte layer202, and a negative electrode 203. The electrolyte layer 202 is disposedbetween the positive electrode 201 and the negative electrode 203.

The positive electrode 201 contains a positive electrode active materialparticle 204 and a solid electrolyte particle 100.

The electrolyte layer 202 contains an electrolyte material (for example,a solid electrolyte material).

The negative electrode 203 contains a negative electrode active materialparticle 205 and a solid electrolyte particle 100.

The solid electrolyte particle 100 is a particle containing the solidelectrolyte material according to the first embodiment as a maincomponent. Here, the particle containing the solid electrolyte materialaccording to the first embodiment as a main component means a particlein which the most abundant component in terms of mass proportion is thesolid electrolyte material according to the first embodiment. The solidelectrolyte particle 100 may be a particle consisting of the solidelectrolyte material according to the first embodiment.

The positive electrode 201 contains a material that can occlude andrelease metal ions (for example, lithium ions). The material is, forexample, a positive electrode active material (for example, the positiveelectrode active material particle 204).

Examples of the positive electrode active material are alithium-containing transition metal oxide, a transition metal fluoride,a polyanionic material, a fluorinated polyanionic material, a transitionmetal sulfide, a transition metal oxyfluoride, a transition metaloxysulfide, and a transition metal oxynitride. Examples of thelithium-containing transition metal oxide are LiNi_(1-d-f)Co_(d)Al_(f)O₂(here, 0<d, 0<f, and 0<(d+f)<1) and LiCoO₂.

In order to well disperse the positive electrode active materialparticle 204 and the solid electrolyte particle 100 in the positiveelectrode 201, the positive electrode active material particle 204 mayhave a median diameter of 0.1 μm or more. This good dispersion improvesthe charge and discharge characteristics of the battery 1000. In orderto rapidly diffuse lithium in the positive electrode active materialparticle 204, the positive electrode active material particle 204 mayhave a median diameter of 100 μm or less. The battery 1000 can beoperated at a high output due to the rapid diffusion of lithium. Asdescribed above, the positive electrode active material particle 204 mayhave a median diameter of 0.1 μm or more and 100 μm or less.

In order to well disperse the positive electrode active materialparticle 204 and the solid electrolyte particle 100 in the positiveelectrode 201, the positive electrode active material particle 204 mayhave a median diameter larger than that of the solid electrolyteparticle 100.

In order to increase the energy density and output of the battery 1000,in the positive electrode 201, the ratio of the volume of the positiveelectrode active material particle 204 to the sum of the volumes of thepositive electrode active material particle 204 and the solidelectrolyte particle 100 may be 0.30 or more and 0.95 or less.

In order to increase the energy density and output of the battery 1000,the positive electrode 201 may have a thickness of 10 μm or more and 500μm or less.

The electrolyte layer 202 contains an electrolyte material. Theelectrolyte material may be the solid electrolyte material according tothe first embodiment. The electrolyte layer 202 may be a solidelectrolyte layer.

The electrolyte layer 202 may be constituted of only the solidelectrolyte material according to the first embodiment. Alternatively,the electrolyte layer 202 may be constituted of only a solid electrolytematerial that is different from the solid electrolyte material accordingto the first embodiment.

Examples of the solid electrolyte material that is different from thesolid electrolyte material according to the first embodiment areLi₂MgX′₄, Li₂FeX′₄, Li(Al,Ga,In)X′₄, Li₃ (Al,Ga,In)X′₆, and LiI. Here,X′ is at least one selected from the group consisting of F, Cl, Br, andI.

In the present disclosure, “(A,B,C)” means “at least one selected fromthe group consisting of A, B, and C”.

Hereinafter, the solid electrolyte material according to the firstembodiment is called a first solid electrolyte material. The solidelectrolyte material that is different from the solid electrolytematerial according to the first embodiment is called a second solidelectrolyte material.

The electrolyte layer 202 may contain not only the first solidelectrolyte material but also the second solid electrolyte material. Thefirst solid electrolyte material and the second solid electrolytematerial may be uniformly dispersed. A layer made of the first solidelectrolyte material and a layer made of the second solid electrolytematerial may be stacked along the stacking direction of the battery1000.

In order to prevent short circuit between the positive electrode 201 andthe negative electrode 203 and to increase the output of the battery,the electrolyte layer 202 may have a thickness of 1 μm or more and 100μm or less.

The negative electrode 203 contains a material that can occlude andrelease metal ions (for example, lithium ions). The material is, forexample, a negative electrode active material (for example, the negativeelectrode active material particle 205).

Examples of the negative electrode active material are a metal material,a carbon material, an oxide, a nitride, a tin compound, and a siliconcompound. The metal material may be a single metal or an alloy. Examplesof the metal material are a lithium metal and a lithium alloy. Examplesof the carbon material are natural graphite, coke, graphitizing carbon,carbon fibers, spherical carbon, artificial graphite, and amorphouscarbon. From the viewpoint of capacity density, suitable examples of thenegative electrode active material are silicon (i.e., Si), tin (i.e.,Sn), a silicon compound, and a tin compound.

In order to well disperse the negative electrode active materialparticle 205 and the solid electrolyte particle 100 in the negativeelectrode 203, the negative electrode active material particle 205 mayhave a median diameter of 0.1 μm or more. The good dispersion improvesthe charge and discharge characteristics of the battery. In order torapidly disperse lithium in the negative electrode active materialparticle 205, the negative electrode active material particle 205 mayhave a median diameter of 100 μm or less. The battery can be operated ata high output due to the rapid diffusion of lithium. As described above,the negative electrode active material particle 205 may have a mediandiameter of 0.1 μm or more and 100 μm or less.

In order to well disperse the negative electrode active materialparticle 205 and the solid electrolyte particle 100 in the negativeelectrode 203, the negative electrode active material particle 205 mayhave a median diameter larger than that of the solid electrolyteparticle 100.

In order to increase the energy density and output of the battery 1000,in the negative electrode 203, the ratio of the volume of the negativeelectrode active material particle 205 to the sum of the volumes of thenegative electrode active material particle 205 and the solidelectrolyte particle 100 may be 0.30 or more and 0.95 or less.

In order to increase the energy density and output of the battery 1000,the negative electrode 203 may have a thickness of 10 μm or more and 500μm or less.

In order to enhance the ion conductivity, chemical stability, andelectrochemical stability, at least one selected from the groupconsisting of the positive electrode 201, the electrolyte layer 202, andthe negative electrode 203 may contain the second solid electrolytematerial.

As described above, the second solid electrolyte material may be ahalide solid electrolyte. Examples of the halide solid electrolyte areLi₂MgX′₄, Li₂FeX′₄, Li(Al,Ga,In)X′₄, Li₃(Al,Ga,In)X′₆, and LiI. Here, X′is at least one selected from the group consisting of F, Cl, Br, and I.

The second solid electrolyte material may be a sulfide solidelectrolyte.

Examples of the sulfide solid electrolyte are Li₂S—P₂S₅, Li₂S—SiS₂,Li₂S—B₂S₃, Li₂S—GeS₂, Li_(3.25)Ge_(0.25)P_(0.75)S₄, and Li₁₀GeP₂S₁₂.

The second solid electrolyte material may be an oxide solid electrolyte.

Examples of the oxide solid electrolyte are:

(i) an NASICON-type solid electrolyte, such as LiTi₂(PO₄)₃ or itselement substitute;

(ii) a perovskite-type solid electrolyte, such as (LaLi)TiO₃;

(iii) an LISICON-type solid electrolyte, such as Li₁₄ZnGe₄O₁₆, Li₄SiO₄,LiGeO₄, or its element substitute;

(iv) a garnet-type solid electrolyte, such as Li₇La₃Zr₂O₁₂ or itselement substitute; and

(v) Li₃PO₄ or its N-substitute.

The second solid electrolyte material may be an organic polymer solidelectrolyte.

Examples of the organic polymer solid electrolyte are a polymer compoundand a compound of a lithium salt. The polymer compound may have anethylene oxide structure. A polymer compound having an ethylene oxidestructure can contain a large amount of a lithium salt and can thereforefurther enhance the ion conductivity.

Examples of the lithium salt are LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiSO₃CF₃,LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiN(SO₂CF₃)(SO₂C₄F₉), and LiC(SO₂CF₃)₃. Onelithium salt selected from these salts may be used alone. Alternatively,a mixture of two or more lithium salts selected from these salts may beused.

At least one selected from the group consisting of the positiveelectrode 201, the electrolyte layer 202, and the negative electrode 203may contain a nonaqueous electrolyte liquid, a gel electrolyte, or anionic liquid for the purpose of facilitating the transfer of lithiumions and improving the output characteristics of the battery 1000.

The nonaqueous electrolyte liquid contains a nonaqueous solvent and alithium salt dissolved in the nonaqueous solvent.

Examples of the nonaqueous solvent are a cyclic carbonate ester solvent,a chain carbonate ester solvent, a cyclic ether solvent, a chain ethersolvent, a cyclic ester solvent, a chain ester solvent, and a fluorinesolvent. Examples of the cyclic carbonate ester solvent are ethylenecarbonate, propylene carbonate, and butylene carbonate. Examples of thechain carbonate ester solvent are dimethyl carbonate, ethyl methylcarbonate, and diethyl carbonate. Examples of the cyclic ether solventare tetrahydrofuran, 1,4-dioxane, and 1,3-dioxolane. Examples of thechain ether solvent are 1,2-dimethoxyethane and 1,2-diethoxyethane. Anexample of the cyclic ester solvent is y-butyrolactone. An example ofthe chain ester solvent is methyl acetate. Examples of the fluorinesolvent are fluoroethylene carbonate, methyl fluoropropionate,fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylenecarbonate. One nonaqueous solvent selected from these solvents may beused alone. Alternatively, a mixture of two or more nonaqueous solventsselected from these solvents may be used.

Examples of the lithium salt are LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiSO₃CF₃,LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiN(SO₂CF₃)(SO₂C_(b 4)F₉), andLiC(SO₂CF₃)₃. One lithium salt selected from these salts may be usedalone. Alternatively, a mixture of two or more lithium salts selectedfrom these salts may be used.

The concentration of the lithium salt is, for example, within a range of0.5 mol/L or more and 2 mol/L or less.

As the gel electrolyte, a polymer material impregnated with a nonaqueouselectrolyte liquid can be used. Examples of the polymer material arepolyethylene oxide, polyacrylonitrile, polyvinylidene fluoride,polymethyl methacrylate, and a polymer having an ethylene oxide bond.

Examples of the cation included in the ionic liquid are:

(i) an aliphatic chain quaternary salt, such as tetraalkylammonium andtetraalkylphosphonium;

(ii) an alicyclic ammonium, such as pyrrolidiniums, morpholiniums,imidazoliniums, tetrahydropyrimidiniums, piperaziniums, andpiperidiniums; and

(iii) a nitrogen-containing heterocyclic aromatic cation, such aspyridiniums and imidazoliums.

Examples of the anion included in the ionic liquid are PF6⁻, BF₄ ⁻, SbF₆⁻, AsF₆ ⁻, SO₃CF₃ ⁻, N(SO₂CF₃)₂ ⁻, N(SO₂C₂F₅)₂ ⁻, N(SO₂CF₃)(SO₂C₄F₉)⁻,and C(SO₂CF₃)₃ ⁻.

The ionic liquid may contain a lithium salt.

At least one selected from the group consisting of the positiveelectrode 201, the electrolyte layer 202, and the negative electrode 203may contain a binder for the purpose of improving the adhesion betweenindividual particles.

Examples of the binder are polyvinylidene fluoride,polytetrafluoroethylene, polyethylene, polypropylene, an aramid resin,polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylicacid, polyacrylic acid methyl ester, polyacrylic acid ethyl ester,polyacrylic acid hexyl ester, polymethacrylic acid, polymethacrylic acidmethyl ester, polymethacrylic acid ethyl ester, polymethacrylic acidhexyl ester, polyvinyl acetate, polyvinylpyrrolidone, polyether,polyether sulfone, hexafluoropolypropylene, styrene butadiene rubber,and carboxymethyl cellulose. A copolymer can also be used as the binder.Examples of such the binder are copolymers of two or more materialsselected from the group consisting of tetrafluoroethylene,hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether,vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene,pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, andhexadiene. A mixture of two or more selected from these materials may beused as the binder.

At least one selected from the positive electrode 201 and the negativeelectrode 203 may contain a conductive assistant for the purpose ofenhancing the electron conductivity.

Examples of the conductive assistant are:

(i) graphites, such as natural graphite and artificial graphite;

(ii) carbon blacks, such as acetylene black and Ketjen black;

(iii) conductive fibers, such as carbon fibers and metal fibers;

(iv) carbon fluoride;

(v) metal powders, such as aluminum;

(vi) conductive whiskers, such as zinc oxide and potassium titanate;

(vii) a conductive metal oxide, such as titanium oxide; and

(viii) a conductive polymer compound, such as polyaniline, polypyrrole,and polythiophene. In order to reduce the cost, the conductive assistantof the above (i) or (ii) may be used.

Examples of the shape of the battery according to the second embodimentare coin type, cylindrical type, square type, sheet type, button type,flat type, and stack type.

The battery according to the second embodiment may be manufactured by,for example, providing a material for forming a positive electrode, amaterial for forming an electrolyte layer, and a material for forming anegative electrode and producing a stack of a positive electrode, anelectrolyte layer, and a negative electrode disposed in this order by aknown method.

EXAMPLES

The present disclosure will now be described in more detail withreference to Examples.

Example 1 Production of Solid Electrolyte Material

LiCl, LiBr, YCl₃, SmCl₃, and CaBr₂ were provided as raw material powderssuch that the LiCl:LiBr:YCl₃:SmCl₃:CaBr₂ molar ratio was about1:1.8:0.8:0.2:0.1 in an argon atmosphere having a dew point of −60° C.or less and an oxygen concentration of 0.0001 vol % or less(hereinafter, referred to as “dry argon atmosphere”). These materialswere pulverized and mixed in a mortar. The resulting mixture washeat-treated in an alumina crucible at 500° C. for 1 hour and was thenpulverized in a mortar. Thus, a solid electrolyte material of Example 1was obtained.

Composition Analysis of Solid Electrolyte Material

The contents of Li, Ca, Sm, and Y per unit weight of the solidelectrolyte material of Example 1 were measured with a high-frequencyinductively coupled plasma emission spectrometer (manufactured by ThermoFisher Scientific, Inc., iCAP7400) by high-frequency inductively coupledplasma emission spectrometry. The contents of Br and Cl in the solidelectrolyte material of Example 1 were measured with an ionchromatography apparatus (manufactured by Dionex, ICS-2000) by an ionchromatography method. The Li:Ca:Y:Sm:Br:Cl molar ratio was calculatedbased on the contents of Li, Ca, Y, Sm, Br, and Cl obtained from thesemeasurement results. As a result, the solid electrolyte material ofExample 1 had a Li:Ca:Y:Sm:Br:Cl molar ratio of3.07:0.10:0.80:0.20:1.80:3.75.

The ratio of the mass of O to the mass of the entire solid electrolytematerial of Example 1 was measured with an oxygen nitrogen hydrogenanalyzer (manufactured by HORIBA, Ltd., EMGA-930) by a nondispersiveinfrared absorption method. As a result, the mass proportion of O was0.03%. Based on this, the (Y+Sm):O molar ratio was calculated. As aresult, the solid electrolyte material of Example 1 had a (Y+Sm):O molarratio of 1.00:0.01.

In the composition analysis, an element of which the molar fractionrelative to the sum of Y and Sm was less than 0.01% was recognized as animpurity. X-ray diffraction

The X-ray diffraction pattern of the solid electrolyte material ofExample 1 was measured with an X-ray diffractometer (manufactured byRIGAKU Corporation, MiniFlex 600) in a dry environment having a dewpoint of −45° C. or less. As the X-ray source, Cu-Kα rays (wavelength:1.5405 angstrom and 1.5444 angstrom) were used.

As the results of the X-ray diffraction measurement, there were peaks at15.43°, 16.80°, 22.90°, 28.67°, 30.59°, 32.76°, 39.80°, 47.55°, and52.05°. FIG. 2 is a graph showing an X-ray diffraction pattern of thesolid electrolyte material of Example 1.

Evaluation of Ion Conductivity

FIG. 3 is a schematic view of a compression molding die 300 used forevaluation of the ion conductivity of a solid electrolyte material. Thecompression molding die 300 included a punch upper part 301, a framemold 302, and a punch lower part 303. The frame mold 302 was made ofinsulating polycarbonate. The punch upper part 301 and the punch lowerpart 303 were both made of electron-conductive stainless steel.

The ion conductivity of the solid electrolyte material of Example 1 wasmeasured using the compression molding die 300 shown in FIG. 3 by thefollowing method.

A powder of the solid electrolyte material of Example 1 was loaded inthe compression molding die 300 in the dry argon atmosphere. A pressureof 400 MPa was applied to the solid electrolyte material of Example 1(i.e., powder 101 of the solid electrolyte material in FIG. 3 ) insidethe compression molding die 300 using the punch upper part 301 and thepunch lower part 303.

While applying the pressure, the punch upper part 301 and the punchlower part 303 were connected to a potentiostat (manufactured byPrinceton Applied Research, VersaSTAT4). The punch upper part 301 wasconnected to the working electrode and the potential measurementterminal. The punch lower part 303 was connected to the counterelectrode and the reference electrode. The impedance of the solidelectrolyte material of Example 1 was measured by an electrochemicalimpedance measurement method at room temperature.

FIG. 4 is a graph showing a Cole-Cole plot obtained by the impedancemeasurement of the solid electrolyte material of Example 1.

In FIG. 4 , the real value of impedance at the measurement point wherethe absolute value of the phase of the complex impedance was thesmallest was regarded as the resistance value of the solid electrolytematerial of Example 1 to ion conduction. Regarding the real value, seethe arrow R_(SE) shown in FIG. 4 . The ion conductivity was calculatedusing the resistance value based on the following mathematicalexpression (1):

σ=(R _(SE) ×S/t)⁻¹   (1).

Here, σ represents ion conductivity; S represents the contact area of asolid electrolyte material with the punch upper part 301 (equal to thecross-sectional area of the hollow part of the frame mold 302 in FIG. 3); R_(SE) represents the resistance value of the solid electrolytematerial in impedance measurement; and t represents the thickness of thesolid electrolyte material applied with a pressure (equal to thethickness of the layer formed from the powder 101 of the solidelectrolyte material in FIG. 3 ).

The ion conductivity of the solid electrolyte material of Example 1measured at 25° C. was 3.0×10⁻³ S/cm. Production of battery

The solid electrolyte material of Example 1 and LiCoO₂ as an activematerial were provided at a volume ratio of 70:30 in the dry argonatmosphere. These materials were mixed in an agate mortar. Thus, amixture was obtained.

The solid electrolyte material (100 mg) of Example 1, the above mixture(12.0 mg), and an aluminum powder (14.7 mg) were stacked in this orderin an insulating tube having an inner diameter of 9.5 mm. A pressure of300 MPa was applied to this stack to form a first electrode and a solidelectrolyte layer. The solid electrolyte layer had a thickness of about500 μm.

Subsequently, metal In foil was stacked on the solid electrolyte layer.The solid electrolyte layer was sandwiched between the metal In foil andthe first electrode. The metal In foil had a thickness of 200 μm.Subsequently, a pressure of 80 MPa was applied to the metal In foil toform a second electrode.

A current collector made of stainless steel was attached to the firstelectrode and the second electrode, and current collecting lead was thenattached to the current collector. Finally, the inside of the insulatingtube was isolated from the outside atmosphere using an insulatingferrule to seal the inside of the tube. Thus, a battery of Example 1 wasobtained. Charge and discharge test

FIG. 5 is a graph showing the initial discharge characteristics of thebattery of Example 1. A charge and discharge test was performed asfollows.

The battery of Example 1 was placed in a thermostatic chamber of 25° C.

The battery of Example 1 was charged with a current density of 86 μA/cm²until the voltage reached 3.7 V. The current density corresponds to 0.05C rate.

Subsequently, the battery of Example 1 was discharged at a currentdensity of 86 μA/cm² until the voltage reached 1.9 V.

As the results of the charge and discharge test, the battery of Example1 had an initial discharge capacity of 515 μAh.

Examples 2 to 4

In Example 2, the solid electrolyte material of Example 1 was left tostand in a dry atmosphere having a dew point of −30° C. and an oxygenconcentration of 20.9 vol % for about 30 minutes. Subsequently, thesolid electrolyte material was heat-treated in the dry argon atmosphereat 500° C. for 1 hour and was then pulverized in a mortar. Thus, a solidelectrolyte material of Example 2 was obtained.

In Example 3, a solid electrolyte material of Example 3 was obtained asin Example 2 except that the time during which the solid electrolytematerial of Example 1 was left to stand in a dry atmosphere having a dewpoint of −30° C. and an oxygen concentration of 20.9 vol % was set to 2hours instead of about 30 minutes.

In Example 4, a solid electrolyte material of Example 4 was obtained asin Example 2 except that the time during which the solid electrolytematerial of Example 1 was left to stand in a dry atmosphere having a dewpoint of −30° C. and an oxygen concentration of 20.9 vol % was set to 80hours instead of about 30 minutes.

The element ratio (molar ratio), X-ray diffraction, and ion conductivityof each of the solid electrolyte materials of Examples 2 to 4 weremeasured as in Example 1. The measurement results are shown in Tables 1and 2. FIG. 2 is a graph showing X-ray diffraction patterns of the solidelectrolyte materials of Examples 2 to 4.

The mass proportions of oxygen to the respective entire solidelectrolyte materials of Examples 2 to 4 were 0.13%, 0.31%, and 1.58%.

Batteries of Examples 2 to 4 were obtained as in Example 1 using thesolid electrolyte materials of Examples 2 to 4.

A charge and discharge test was implemented as in Example 1 using thebatteries of Examples 2 to 4.

The batteries of Examples 2 to 4 were well charged and discharged as inthe battery of Example 1.

Comparative Example 1

LiCl and FeCl₂ were provided as raw material powders such that theLiCl:FeCl₂ molar ratio was about 2:1 in the dry argon atmosphere. Thesematerials were subjected to milling treatment using a planetary ballmill at 600 rpm for 25 hours for mechanochemical reaction. Thus, a solidelectrolyte material of Comparative Example 1 was obtained. The solidelectrolyte material of Comparative Example 1 was a known halide solidelectrolyte material having a composition represented by Li₂FeCl₄.

The ion conductivity of the solid electrolyte material of ComparativeExample 1 was measured as in Example 1. As a result, the ionconductivity measured at 22° C. was 9.0×10⁻⁶ S/cm.

A battery of Comparative Example 1 was obtained as in Example 1 usingthe solid electrolyte material of Comparative Example 1.

A charge and discharge test was implemented as in Example 1 using thebattery of Comparative Example 1. The battery of Comparative Example 1had an initial discharge capacity of only 1 μAh or less. That is, thebattery of Comparative Example 1 was neither charged nor discharged.

TABLE 1 Element ratio (molar ratio) Ion conductivity Li Ca Y Sm Br Cl O(S/cm) Example 1 3.07 0.10 0.80 0.20 1.80 3.75 0.01 3.0 × 10⁻³ Example 23.10 0.10 0.80 0.20 1.88 3.94 0.04 2.7 × 10⁻³ Example 3 2.99 0.10 0.800.20 1.68 3.59 0.08 1.2 × 10⁻³ Example 4 3.03 0.10 0.80 0.20 1.37 3.020.36 4.4 × 10⁻⁵ Comparative Li₂FeCl₄ 9.0 × 10⁻⁶ Example 1

TABLE 2 X-ray diffraction peak position (2θ (deg)) Example 1 — 15.4316.80 22.90 28.67 30.59 32.76 39.80 47.55 52.05 — — Example 2 14.2615.43 16.81 22.91 28.70 30.56 32.72 39.74 47.54 52.02 — 59.36 Example 3— 15.43 16.77 22.87 28.66 30.55 32.68 39.70 47.54 52.02 57.58 — Example4 14.29 15.44 16.80 22.90 28.70 30.56 32.68 39.72 47.54 52.01 57.5959.36

Consideration

As obvious from Table 1, the solid electrolyte materials of Examples 1to 4 each have a high ion conductivity of 1×10⁻⁵ S/cm or more at aroundroom temperature.

As obvious from Examples 1 to 4, when the molar ratio of O to the sum ofY and

Sm is greater than 0 and 0.36 or less, the solid electrolyte materialhas a high ion conductivity of 1×10⁻⁵ S/cm or more. As obvious bycomparing Examples 1 to 3 with Example 4, when the molar ratio isgreater than 0 and 0.08 or less, the solid electrolyte material has ahigher ion conductivity of 1×10⁻³ S/cm or more.

As obvious from the X-ray diffraction patterns shown in FIG. 2 and fromTable 2, the crystal structure of a solid electrolyte material changesdepending on the content of O. The contents of Br and Cl decrease withan increase in the content of O. Accordingly, it is inferred that O wassubstituted with Br and Cl and was incorporated into the crystalstructure.

The batteries of Examples 1 to 4 were charged and discharged at 25° C.

Since the solid electrolyte materials of Examples 1 to 4 do not containsulfur, hydrogen sulfide does not occur.

As described above, the solid electrolyte material of the presentdisclosure has a high lithium ion conductivity and is suitable forproviding a battery that can be well charged and discharged.

The solid electrolyte material of the present disclosure is used in, forexample, an all solid lithium ion secondary battery.

What is claimed is:
 1. A solid electrolyte material consistingessentially of Li, Ca, Y, Sm, X, and O, wherein X is at least oneselected from the group consisting of F, Cl, Br, and I.
 2. The solidelectrolyte material according to claim 1, wherein X is Cl and Br. 3.The solid electrolyte material according to claim 1, further comprising:at least one selected from the group consisting of Gd, Sr, Ba, Al, Sc,Ga, Bi, La, Zr, Hf, Ta, and Nb.
 4. The solid electrolyte materialaccording to claim 1, wherein an X-ray diffraction pattern obtained byX-ray diffraction measurement using Cu-Kα rays includes peaks indiffraction angle 2θ ranges of 14.9° or more and 16.0° or less, 16.2° ormore and 17.4° or less, 22.3° or more and 23.5° or less, 28.1° or moreand 29.2° or less, 30.0° or more and 31.2° or less, 32.1° or more and33.3° or less, 39.2° or more and 40.3° or less, 47.0° or more and 48.1°or less, and 51.5° or more and 52.6° or less.
 5. The solid electrolytematerial according to claim 1, wherein following four mathematicalexpressions are satisfied:2.6≤x≤3.4;0.09≤y≤0.11;1.2≤z≤2.1; and2.7≤w≤4.4, wherein x represents a molar ratio of Li to the sum of Y andSm; y represents a molar ratio of Ca to the sum of Y and Sm; zrepresents a molar ratio of Br to the sum of Y and Sm; and w representsa molar ratio of Cl to the sum of Y and Sm.
 6. The solid electrolytematerial according to claim 1, wherein a molar ratio of O to the sum ofY and Sm is greater than 0 and 0.36 or less.
 7. A battery comprising: apositive electrode; a negative electrode; and an electrolyte layerdisposed between the positive electrode and the negative electrode,wherein at least one selected from the group consisting of the positiveelectrode, the negative electrode, and the electrolyte layer containsthe solid electrolyte material according to claim 1.